Minnesota health officials said Monday they have confirmed another case of measles, bringing the total number of children sickened by the current outbreak to nine.

All the infected children were unvaccinated for measles, and most of the cases have occurred in the Somali-American community, where vaccination rates have been relatively low.

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State health investigators are still trying to determine the source of the outbreak, which most likely involved a traveler to a foreign country who brought back the infection.

Measles is considered eradicated in the United States, although small numbers of cases pop up each year.

Measles is a highly infectious disease that can easily spread by coughs and sneezes to those without immunity protection.

Symptoms almost mimic those of a cold, including runny nose, cough, watery eyes and a fever. But after four days a distinctive rash typically develops on the head and spreads to the rest of the body. In some cases, the illness requires hospital treatment.

This is the largest measles outbreak in Minnesota since 2011, when 26 people were infected.